随机练习：C#实现维吉尼亚加密与解密（解密前提为已知密匙）

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Linq;
 using System.Text;
 using System.Windows.Forms;

 namespace Vigenere
 {
     public partial class Form1 : Form
     {
         private string[,] matrix = new string[, ];
         private ASCIIEncoding ascii = new ASCIIEncoding();

         //key
         private string key;
         //code
         private string code;
         //text
         private string text;

         public Form1()
         {
             InitializeComponent();
             #region Generate Virginia Martix
             for (int i = ; i < ; i++)
             {
                 for (int j = ; j < ; j++)
                 {
                     int number =  + i + j;
                     if (number > )
                     {
                         number -= ;
                     }
                     byte[] bt = new byte[] { (byte)number };
                     matrix[i, j] = ascii.GetString(bt);
                 }
             }
             #endregion
         }
         //加密
         private void button1_Click(object sender, EventArgs e)
         {
             key = this.txtKey.Text.ToString().ToUpper();
             code = "";
             text = this.txtText.Text.ToString().ToUpper();
             List<int> keyNum = new List<int>(); ;

             for (int i = ; i < key.Length; i++)
             {
                 string str = key.Substring(i, );
                 keyNum.Add((int)ascii.GetBytes(str)[] - );
             }

             int index = -;
             for (int i = ; i < this.text.Length; i++)
             {
                 if (this.text.Substring(i, ).ToString() == " ")
                 {
                     code += " ";
                     continue;
                 }
                 index++;
                 code += matrix[keyNum[index % key.Length], (int)ascii.GetBytes(this.text.Substring(i, ))[] - ];
             }

             this.txtCode.Text = code.ToString();
         }
         //解密
         private void button2_Click(object sender, EventArgs e)
         {
             key = this.txtKey.Text.ToString().ToUpper();
             code = this.txtCode.Text.ToString().ToUpper();
             text = "";
             List<int> keyNum = new List<int>(); ;

             for (int i = ; i < key.Length; i++)
             {
                 string str = key.Substring(i, );
                 keyNum.Add((int)ascii.GetBytes(str)[] - );
             }

             int index = -;
             for (int i = ; i < this.code.Length; i++)
             {
                 if (this.code.Substring(i, ).ToString() == " ")
                 {
                     text += " ";
                     continue;
                 }
                 index++;

                 for (int j = ; j < ; j++)
                 {
                     if (this.code.Substring(i, ).ToString() == matrix[keyNum[index % key.Length], j])
                     {
                         byte[] bt = new byte[] { (byte)(j + ) };
                         text += ascii.GetString(bt);
                     }
                 }
             }

             this.txtText.Text = text.ToString();
         }
     }
 }

对于维吉尼亚方阵及运用维吉尼亚方阵的加密与解密，可参考http://baike.baidu.com/view/270838.htm?fromTaglist

画面结果如下：